This project is concerned with hearing loss associated with aging and with exposure to low levels of noise. Five projects are planned. Project #1 proposes to develop an animal model of presbyacusis and to study hypothesized interactions between aging effects and exposure to noise. Project #2 is a clinical study of human presbyacusis and control subjects with the major purpose being to categorize or develop profiles of presbyacusis that are based on current audiological-otological-medical information. Project #3 addresses the pathophysiology of presbyacusis by examining the physiology of the endolymphatic duct, and the neurophysiology of the auditory nerve and brainstem. Project #4 focuses on the histopathology of the cochlea, particularly the sensory and supporting cells, stria vascularis, and spiral ligament, including vasculature. Project #5 is a histochemical study of the cochlea which extends Project #4 by providing precise information about the presence and distribution of specific molecular constituents in the cochlea. Experimental animals are Mongolian gerbils who are born are born and reared in a quiet, acoustically controlled environment. Project #1 provides experimental animals for Projects 3, 4, and 5. Thus, a given animal is studied with respect to cochlear physiology, neurophysiology of the auditory nerve and brainstem, and cochlear histopathology and histochemistry. These extensive animal data in combination with clinical and experimental data from the humans of Project #2 provide a comprehensive program of research on presbyacusis and hearing loss in general.